I'd say the correct answer is: Race by HR, RPE, and Power. Of course you have to start somewhere near your historically-established threshold, but on race day, you have to find what the day allows you. From there it is a matter of holding the razor's edge for 45-48 minutes. If you paced it right, you won't be able to increase power by much leading toward the finish.

Targeting some specific power number or HR won't work. It never will. You have to listen to your body on race day. You may be able to exceed your power that you might have targeted otherwise. Or . . . worst case . . . you might think you can (or should) hold a higher power and find yourself blown up.